1. Field of the Invention
The present invention relates to the protected storage of data on optically-readable media.
2. Description of the Related Art
A variety of optically-readable media are known in the art for storing and selectively retrieving digital data. Optically-readable media typically have a circular or disc-like form factor, and may be referred to interchangeably as “optical media,” “optical discs,” or “optical storage discs.” The CD is among the earliest developed and most commonly available optical medium. Data is usually stored on an optical disc in a digitally encoded format as a series of tiny indentations (“pits”) alternating with higher-elevation “lands,” in a tightly packed spiral. The digitally encoded data is commonly encrypted, as well. These media are readable by a variety of different optical devices or “drives,” including a variety of CD and DVD drives, CD and DVD decoders in home entertainment systems, video game consoles, and automobile navigation systems. An optical drive includes a reader head capable of focusing a laser or other beam of light on an optical storage disc to read the digitally encoded data. The difference in height between pits and lands leads to a phase difference between the light reflected from a pit and from its surrounding land. This optical behavior is processed electronically by the optical drive to correctly read the stored data.
Optical disc technology has been expanded to include not only the fixed storage of music and video files, but also editable or “writeable” formats also capable of storing other types of electronic data or computer “files.” Writeable and re-writeable version of optical discs currently include CD-R, CD-RW, DVD, DVD-R, and DVD-RW. Emerging technology in optical media includes Blue-Ray discs, named for the blue-violet laser used to read and write this type of disc, as well as High-Density/High-Definition DVD (HD DVD). Some optical discs, such as dual-layer DVDs, store optically-readable data on at least two layers. One or more of the layers may be semi-transparent, to allow the reader head to focus its light beam on the desired layer to be read. It is reasonable to expect the possibility of currently available or future developed optical media to include more than two layers.
Despite the rapid and significant advances in optical media technology, today's optical media discs are not without limitations. Presently available optical discs have read/write surfaces in plain view of an optical reader head. Thus, all the actual raw data (encrypted or not) on an optical disc can potentially be viewed/read by anyone having access to a conventional optical drive. Even encrypted data may potentially be copied, such as using “bit-by-bit” or other brute-force techniques. For example, an unauthorized disc replicator can replicate an encrypted movie DVD in a format readable on DVD players, even without knowing the encryption algorithm used to decrypt the digitally encoded data. Even multi-layer discs have their data written contiguously on each layer, making it easy for one to obtain and/or copy data from different layers.
In view of the limitations and disadvantages of currently-available optical media technology, methods and devices are needed for better and more secure storage and retrieval of data on optical media. It would be desirable for the improved methods and devices to provide increased protection against unauthorized reading and/or copying of data, while incorporating at least some aspects of existing optical media technology, such as the use of a focused beam of light to read data.